Conventional thermoforming is accomplished by utilization of a flat die surface having the number and type of cavities required in it and by placing a sheet of semi-molten film directly over top of the die and applying either pressure or vacuum or both to form the film to the shape of the cavity. It is even more desirable to provide a continuous process in which a web of film may be continuously extruded and utilized by mold cavities. It is highly desirable to extrude the film web at a constant speed in order to closely control crystallization, thickness, degree of crystallinity, etc. The problem then becomes the matching of the constant film speed to that of the surface speed of the die cavities. It is generally not possible to manufacture die cavities in the surface of a truly cylindrical surface, and it is, therefore, necessary to construct a drum with several flat faces on it, each of which contains a number of cavities on which to vacuum or pressure form articles. If such a multifaced drum is driven at a constant rotational speed, the web of film which issues from the film die at a constant translational speed will vary in thickness on contact with the drum as the radius, and, hence, the tangential velocity of the drum varies where it is contacted by the film. To solve this problem, it would be necessary to provide an expensive and complicated variable speed drive transmission to drive the drum so that the surface velocities would be constant at the point of film tangency. The instant invention provides a simple and unique means to continuously vary the rotational speed of a multifaced vacuum forming drum with any number of faces such that if a web of hot film were extruded at a constant rate, the rotational speed of the drum would vary as required to accept this film at approximately said constant rate.